In the chlorination of titanium-containing raw materials, particularly ilmenite, there is formed in great quantity a mixture of solid, dust-forming, chlorides containing an iron chloride. This mixture of chlorides will be referred to as "chlorination dust" hereinbelow. The chlorination dust contains, in addition to iron (II) chloride and/or iron (III) chloride, other chlorides such as, for example, chlorides of vanadium and chromium, small amounts of titanium tetrachloride and HCl as well as cokes, titanium-containing starting material and additional substances, which are carried over from the chlorination reactor.
The solids mixture of chlorination dust often displays itself in the form of a very fine dust, which builds a chloride mist in the atmosphere. It possesses a low density. Also, the chlorides of vanadium and chromium are poisonous and water soluble. The chlorination dust material is, therefore, badly transportable in the existing form and can only be stored with difficulty.
It is proposed in U.S. Pat. No. 3,655,344 that the solid mixture of chlorination dust be treated with water and the chromium and vanadium thereby dissolved out, and from the resulting solution, through addition of an alkaline substance, chromium and vanadium be precipitated. The treatment with water and the addition of the alkaline substance can take place simultaneously.
In accordance with U.S. Pat. No. 3,696,519 the solids mixture of chlorination dust is mixed with carbonates of alkaline or alkaline earth metals to tie-up the evolution of fumes. Calcium oxide is ineffective according to this patent.
Also, U.S. Pat. No. 3,867,515 describes a process in which the solids mixture of chlorination dust is made into pellets during addition of water or aqueous solutions or alkali suspensions or acidic substances.
The processes described in the above-mentioned patents are indeed successful in converting the undesirable ingredients of the solids mixture of chlorination dust into a water insoluble form and in obtaining a transportable and storable product. Each of the described processes is, however, characterized by severe disadvantages. For instance, in the process according to U.S. Pat. No. 3,655,344 the treatment is performed in the presence of great quantities of water; great sediment basins are necessary in which the precipitated compounds can be deposited; and, moreover, a filtration step is necessary. According to U.S. Pat. No. 3,696,519 the resulting product is finely divided and therefore difficult to transport; and, additionally, the process is not successful in freely converting iron (II) chloride into insoluble compounds. The process according to U.S. Pat. No. 3,867,515 requires a separate process step for the dissolution or suspension of the alkali substance which produces higher costs. Additionally, the processes described in the above-mentioned patents cannot be adapted to short-time changes in the falling chlorination dust, for a new solution or suspension of alkaline substances must be readily supplied or made available.
There has now been discovered a new process for the treatment of solids mixtures of chlorination dust comprising mainly iron chlorides obtained in the chlorination of titanium-containing raw materials, particularly ilmenite which avoids or overcomes the disadvantages of the processes described in the above-mentioned patents. The solid mixture of chlorination dust treated in accordance with the process of the invention is converted into a good transportable state and the soluble dangerous transformed metal chlorides, particularly those of vanadium and chromium, are converted into water insoluble compounds such as, for example, into hydroxides or oxides.